1. Field of the Invention
The present invention is related generally to a transportable container for storing substrates such as a semiconductor wafer transportation pod for accommodating a stack of semiconductor wafers. In particular, the present invention is related to a SMIF (Standard Mechanical Interface)-type semiconductor wafer transportation system for accommodating a stack of semiconductor wafers in a SMIF-type box and transporting the stack of semiconductor wafers between the process chambers.
2. Description of the Related Art
It is a very important gist in the semiconductor production line to improve the device yield. The major causes of lessening the device yield is the existence of contaminant particles consisting of dust, organic substances and so forth. In the prior art technique, it is the measure for meeting the contaminant particles problem to conduct the LSI production processes within a clean room. However, the size of the contaminant particles to be eliminated has been decreased along with the miniaturization of LSIs and the rapidly increasing packing densities and therefore it is difficult to furthermore purify the clean room environment itself in view of avoiding an increase in costs. It is therefore proposed to make use of an SMIF-type system provided with a sealed wafer pod in place of an open cassette which has been used in the prior art technique of the semiconductor wafer transportation. By means of the wafer pod, it is possible to maintain dust-free wafers because the wafers can be accepted, transported and stored in a sealed box implemented with the wafer pod. Furthermore, even if the environment around the process chambers is not so purified, it is possible to conduct the wafer transportation between the process chambers with the wafers free from contaminant particles.
FIG. 1A is a schematic diagram showing the wafer transportation by means of a semiconductor wafer transportation pod which is placed on a wafer pod table 20 for carrying in or out the semiconductor wafers 10. As illustrated in FIG. 1A, in the case of the prior art semiconductor wafer transportation pod, the pod lid 14b is detached from the wafer pod body 12 when the wafers 10 are carried out from the semiconductor wafer transportation pod and carried in an semiconductor process chamber (not shown in the figure). The detachment of the pod lid 14b is performed by means of a lid opening/closing control means 22 provided with a pod lid shutting device 16b. Inversely, when the wafers 10 are carried in the wafer pod body 12 after the wafers 10 have been processed in the semiconductor process chamber, the lid opening/closing control means 22 then serves to attach the pod lid 14b to the wafer pod body 12 in order to sealably close the wafer pod body 12.
On the other hand, in the recent years, there have been demands for protecting the surface of the semiconductor wafers from the generation of natural oxide films by means of the semiconductor wafer transportation pod in addition to demands for excluding contaminant particles. The natural oxide films are undesirable resulting in unexpected troubles during a process so that it is desirable to be able to avoid the formation thereof. Particularly, substantial adverse effects are likely in the case of highly miniaturized LSIs. Because of this, for the purpose of avoiding the generation of natural oxide films, it is proposed to fill the wafer pod with an inactive gas such as nitrogen (N2), argon (Ar) and so forth and to transport the wafer pod as it is.
Namely, as illustrated in FIG. 1B, an inactive gas such as nitrogen is injected into the wafer pod body 12 through the attachment 18 after sealing and fixing the pod lid 14b to the wafer pod body 12. The wafer pod is then transported with the atmosphere of the inactive gas inside of the wafer pod body 12. The surfaces of the semiconductor wafers 10 shall not be exposed to oxygen but only be exposed to nitrogen during the transportation between the process chambers. Accordingly, it is possible to protect the surfaces of the wafers 10 from the generation of natural oxide films. The semiconductor wafers 10 are also protected from the generation of natural oxide films even in the case that the wafer pod is temporarily stored in a stocker together with the semiconductor wafers 10 therein.
However, it takes, for example, about 10 minutes to completely fill the wafer pod body 12 with the inactive gas in the case that the semiconductor wafer transportation pod has been designed to accommodate 25 wafer having a diameter of 300 mm.
Because of this, (1) the wafer pod can not be transported to the next semiconductor process chamber just after collecting and transferring the semiconductor wafers 10 into the wafer pod. Namely, the transportation of the wafer pod is delayed by the gas filling time. At the present time, the manufacture process of a semiconductor device is composed of a large number of manufacturing steps in the order of 200 steps, and therefore, if 10 minutes is required for each manufacturing step, it takes about total 33 hours required of the gas filling time for the entire 200 manufacturing steps. Accordingly, there is a problem that the cycle time required for completing all the manufacturing steps is elongated by the gas filling time resulting in deteriorating the effectiveness of the manufacture process, and then an increase in costs.
Furthermore, (2) the next wafer pod can not be placed on the wafer pod table 20 during the period that the previous wafer pod is being filled with the gas. Namely, the process of the next wafer pod is therefore delayed by the gas filling time of the previous wafer pod. On the other hand, the semiconductor process chamber of the subject manufacturing step is left idling during the period that the previous wafer pod is being filled with the gas so that the process chamber is used in an ineffective manner. The accumulated loss time is considered to be substantial. Furthermore, even if there are a plurality of the wafer pod tables 20 available in the system, it is the case that all the wafer pod tables 20 are in use. In this case, the process of a wafer pod as transported is delayed until one of the wafer pods has been completely filled with the gas. Accordingly, in the same manner as the above (1), it results in elongating the cycle time required for completing all the manufacture process and deteriorating the effectiveness of the manufacture process, and then an increase in costs.